In the fire protection industry, fire sprinklers are designed for various residential and storage applications in accordance with accepted industry standards. These standards include, for example, the Standard for the Installation of Sprinkler Systems, NFPA 13, issued by the National Fire Protection Association, and Standard 199, issued by Underwriters Laboratories, Inc. Existing versions of both standards and all prior, superseded versions of both standards are incorporated by reference herein.
NFPA-13 defines various requirements for sprinkler systems used in occupied commercial or residential interior spaces or “occupancies” with different fire hazard potentials. In particular, the standard recognizes three general hazard categories for sprinkler systems: light, ordinary and extra. Light hazard occupancies are those where the quantity and/or combustibility of contents is low and fires with relatively low rates of heat release are expected. Ordinary hazard occupancies are those where the quantity and/or combustibility of contents is equal to or greater than that of light hazard, ranging from low to high, where the quantities of combustibles are moderate and stock piles do not exceed twelve feet, such that fires with moderate to high rates of heat release are expected. Extra hazard occupancies are those where the quantity and combustibility of contents is very high and flammable or combustible liquids, dust, lint or other materials are present, such that the probability of rapidly developing fires with high rates of heat release is very high.
The present invention is directed to the protection of ordinary hazard occupancies, in both commercial and residential environments, although it may also be advantageously applied to light hazard occupancies.
Standard coverage ordinary hazard sprinklers generally protect a maximum coverage area of 130 square feet. According to the guidelines in NFPA 13, extended coverage ordinary hazard sprinklers must protect from 225 to 400 square feet. The present invention is directed to this greater degree of protection, although it may also find use in standard coverage applications.
Each different sprinkler type demands a different type of water spray pattern to achieve either fire control or suppression. The different spray patterns are achieved by varying such factors as the shape of the sprinkler frame, the k-factor and the geometry of the deflector positioned below the frame for creating a spray pattern. The deflector geometry is particularly significant, since the deflector is a main component of the sprinkler assembly and to a great extent defines the size, shape, uniformity and water droplet size of the pattern.
Some conventional sprinkler designs have been characterized by incomplete patterns, lacking water of sufficient density and drop size directly under the sprinkler. This poses a severe problem if the fire should start in this location. To remedy this, other prior art sprinkler designs have peripheral slots in the deflector to permit water to descend down through the slots. However, the shape of the slots in turn caused a reduction in the size of the water drops, a condition commonly referred to as misting or mist. This condition does not provide a pattern of uniform density with water of sufficient velocity beneath the sprinkler to achieve efficient fire control. As a result, some prior art sprinkler systems formed of individual sprinklers in a rectangular layout have used spray patterns that discharge water generally horizontally and/or generally radially outward from the sprinklers in order to provide an overlap of the individual patterns to complete the overall pattern. This setup has been inefficient.
A further difficulty created by the prior art use of adjacent sprinklers with such overlapping patterns arises from the structure used to trigger the start of water delivery. Many sprinklers use a heat-sensitive trigger that starts the flow of water when the ambient temperature reaches a set level. In this way, if a fire is localized, only the sprinklers in the immediate area activate while the more distant sprinklers remain off. This reduces the demand for water and minimizes damage to the contents of the space.
On the other hands, it is then essential that the sprinklers in the immediate area timely activate. It has been found that when the adjacent sprinklers have overlapping horizontal spray patterns, the spray from one sprinkler may impinge on the trigger of an adjacent sprinkler, cooling down that trigger so that the adjacent sprinkler is slow to activate or even fails to activate at all. This represents a serious threat to fire control known as non-operation or “skipping,” resulting in an uncontrolled fire.